The present invention relates to method and apparatus for locally removing a patterned film when the film is to be modified, the film being a mask or reticle used either in a semiconductor integrated circuit or during fabrication of a semiconductor integrated circuit.
For example, a mask which is subject to such an operation could be constituted by a film, or layer, of Cr, Mo, a Cr and chromium oxide film combination, or an Mo and molybdenum oxide film combination, on a glass substrate.
Such procedure can also be performed on a wiring and/or passivation layer on an IC wafer.
A conventional apparatus for modifying a patterned film is shown in FIG. 2, where ions are produced from an ion source 1. The ions are passed through an ion optics including condenser lenses 2 and objective lenses 3 so that the beam 5 is focused to a given radius of less than 1.mu.. Then, the beam passes between scanning electrodes 4 and scans the surface of a sample 6.
An XY stage 7 is moved in accordance with preset data so that a desired portion of the patterned film on the surface of the sample 6 is located immediately below the focused ion beam, or the beam 5 is scanned. Secondary charged particles 8 are emitted from the surface of the sample 6 in response to irradiation by the beam 5. Those particles 8 are detected by a detector 9. The output signal from the detector 9 is fed to an electronic circuit such as an A/D converter 10. The pattern in which the secondary charged particles are detected is displayed on a display device 11. This permits one to observe or check the patterned film with the naked eye. Then, the sample 6 is moved by the XY stage 7 to cause the portion of the film to be removed to fall within the range scanned by the focused ion beam.
The position and the range of the portion of the patterned film to be removed are set. The range scanned by the beam is set, using the scanning electrodes 4 or blanking electrodes 12, in order that the ion beam fall on only a desired portion of the surface of the sample 6 and scan it. In this way, the beam is caused to scan only the desired portion of the patterned film and so the desired portion is repeatedly irradiated. The patterned film on the desired portion is etched away by the ion sputtering. Generally, this requires repeated irradiation of the material to be removed.
FIG. 4 illustrates a sequence in which the focused ion beam is scanned by the prior art techniques. The beam is scanned over an area 24 which is to be modified. The beam is moved across spots 1, 2, 3, . . . , i-1, i, . . . , k-1, k in that order. The same frame of scan is repeated. The beam halts for a given time at each spot. Usually, the distance between successive spots is less than the whole width of the ion beam. The beam shifts momentarily from one spot to the next and, therefore, the raster scan is continuous as a whole. FIG. 5 shows the spatial distribution of the intensity, at the sample surface, of the focused ion beam which scans the line beginning with spot 1 and ending with spot i-1. Spots 1, 2, . . . , i-1 of FIG. 5 correspond to spots 1, 2, . . . , i-1 of FIG. 4. In FIG. 5, when the beam reaches each of spots 1, 2, 3, the region irradiated by the beam assumes distribution curves 1, 2, 3, respectively. As can be seen from FIG. 5, the distribution curves 1, 2, 3 overlap each other.
In the conventional method and apparatus for modifying a patterned film, a desired portion of the film is removed only by sputtering with the focused ion beam. Therefore, it takes a very long time to fully remove the desired portion. As shown in FIG. 3, the pattern formed on a substrate 14 is etched away by sputtering. The material of the patterned film is sputtered on the side walls of a removed portion or on the surroundings. As a result, a deposit 13 is formed. Consequently, the sputtering etching is not done effectively. Further, the speed of removal is low.
A portion of a substrate surface, at which a pattern film is removed by a focused ion beam, is implanted with the ions. Therefore, the quality of the portion of the substrate surface changes. For example, in case the substrate is comprised of a photomask, the transparency deteriorates. And in case the substrate is composed of a semiconductor, the electric characteristics change.